The application generally relates to a high current high power solid state relay. The application relates more specifically to a high current high power solid state relay in a planar metal bus bar and heat dissipating enclosure.
Solid state relays (SSRs) may be based on a single MOSFET or multiple MOSFETs in a paralleled array. SSRs are generally limited in the amount of current, or the ampacity, that the device is capable of switching. Another limitation of SSRs is the lack of electrical isolation between the SSR actuating or gate circuits and the load circuits. However SSRs have an advantage over traditional mechanical relays as traditional relays have slower turn-on and turn-off times.
A MOSFET switch is a three terminal device including source, gate and drain terminals. SSRs in the past were limited by internal resistance present in the MOSFETs between the drain and the source when the device is gated on. Recent technology has reduced the dependency of the devices on the resistance from source to drain, but other physical limitations in the SSR package are still a concern. The relay package resistance due to the leadframe, wire bonds, etc., may limit the performance of the SSR. In high conductivity devices, the external resistances may offset improvements in the MOSFET, as the internal resistance between the drain and the source tends to increase significantly when the temperature of the SSR increases due to high currents. Other solid state devices may also be used to switch current in an SSR, such as SCRs or triacs.
To dissipate temperature increase in the MOSFET, large heat sinks are used for mounting the SSR to dissipate heat produced by the resistance and current. In some instances the heat sinks may permit the MOSFETs to become overheated due to temperature rise in the MOSFET, which can destroy the MOSFETs if the maximum temperature rating is exceeded. One solution is to attempt to lower the resistance between the MOSFET, the source and the load by increasing package component parameters, e.g., connector size, trace width and thickness, and wire gauge, while decreasing other package component parameters, e.g., trace lengths, wire lengths, and connector resistance, within the design parameters of the heat sink.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.